For the formation of amorphous deposited films such as amorphous silicon-containing deposited film, thermal-induced chemical vapor deposition method, plasma CVD method, CVD method, reactive sputtering method, ion plating method, light-induced CVD method, etc. have been tried. Among these methods, the plasma CVD method has been generally recognized as being the most preferred and it is currently used to manufacture amorphous deposited films on a commercial basis.
However, for any of the known amorphous silicon-containing deposited films, even if it is the one obtained by the plasma CVD method, there are still left subjects to make further improvements not only in overall characteristics in view of electrical and optical properties, fatigue resistance upon repeating use and use-environment characteristics, but also in productivity including filmuniformity and reproducibility and mass-productivity.
Further, the operation conditions to be employed in the formation of an amorphous silicon-containing deposited film by the plasma CVD method are much more complicated than any other known CVD methods and it is extremely difficult to generalize them. That is, there already exist a number of variations even in the correlated parameters concerning the temperature of a substrate, the amount and the flow rate of gases to be introduced, the degree of pressure and the high frequency power for forming a film, the structure of an electrode, the structure of a reaction chamber, the rate of flow of exhaust gases, the plasma generation system, etc. Besides said parameters, there also exist other kinds of parameters.
Under these circumstances, in order to obtain a desirable deposited film product, it is required to choose precise parameters from a great number of varied parameters. Sometimes, serious problems occur. Because of the precisely chosen parameters, a plasma is apt to be in an unstable state. This condition often invites problems in a deposited film to be formed.
And for the apparatus in which the process using the plasma CVD method is practiced, its structure will eventually become complicated since the parameters to be employed are precisely chosen as above stated. Whenever the scale or the kind of the apparatus to be used is modified or changed, the apparatus must be so structured as to cope with the precisely chosen parameters.
In this regard, even if a desirable deposited film should be fortuitously mass-produced, the film product becomes unavoidably costly because (1) a heavy investment is firstly necessitated to set up a particularly appropriate apparatus therefor; (2) a number of process operation parameters even for such apparatus still exist and the relevant parameters must be precisely chosen from the existing various parameters for the mass-production of such film. In accordance with such precisely chosen parameters, the process must then be carefully practiced.
Against this background, there is now an increased demand for a method that makes it possible to practice the process at lower temperatures and at a high film-forming rate in a simple apparatus in order to mass-produce a desirable functional deposited film having a relevant uniformity and having many practically applicable characteristics and such that the product will be relatively inexpensive.
In view of the foregoing situations, a film-forming method different from the plasma CVD method, that is, Hydrogen Radical Assisted Chemical Deposition Method (HR-CVD Method) has been proposed as disclosed in Japanese Patent Laid-Open No. Sho 60-41047. In the HR-CVD method, a precursor capable of contributing to formation of a deposited film which is generated in an activation space (B) disposed separately from a film-forming space (A) for forming the deposited film on the surface of a substrate and an active species capable of chemically reacting with said precursor to cause the formation of a deposited film which is generated in other activation space (C) disposed separately from the activation space (B) are introduced respectively and separately into the film-forming space (A) and they are chemically reacted to thereby cause the formation of a deposited film on the substrate.
FIG. 3 schematically shows a typical constitution of an apparatus suitable for practicing the process of forming a deposited film by the HR-CVD method. In FIG. 3, there are shown a deposition chamber 301 having the film-forming space (A), in which are shown a substrate 303 which is disposed on a substrate holder 302, an electric heater 304 for heating the substrate, material gas reservoirs 305 through 308 and 312, pressure controllers 305a through 308a and 312a for the raw material gases, valves 305(a,b) through 308(a,b) and 312(a,b) for supplying respective raw material gases, mass flow controllers 305(d) through 308(d) and 312(d) for controlling the respective flow rates of the respective raw material gases, gas feed pipes 309 and 313 for introducing the respective raw material gases, a microwave power source 310 for generating microwave energy which is supplied through a waveguide 311 and an applicator provided to surround the outer wall face of a tube made of a dielectric material having an activation space C into the said space in order to convert the raw material gase from the feed pipe 309 into an active species. There are also shown an electric furnace 314 provided with a quartz tube 321 having an activation space B so as to surround the outer wall face of the said quartz tube for converting the raw material gas from the feed pipe pipe 313 into a precursor in the said activation space (B), an exhaust valve 315 provided with an exhaust pipe 316. The precursor formed in the activation space (B) and the active species formed in the activation space (C) are chemically reacted in the film-forming space (A) to thereby form a deposited film on the substrate 303.
The foregoing HR-CVD process for forming a deposited film on a substrate provides various advantages which can not be expected by the known plasma CVD process. For example, a desired deposited film may be formed on a substrate maintained at low temperature without generating plasma in the film deposition space but using an active species from the active species generation space and a precursor from the precursor generation space; and the deposited film formed on the substrate is not affected by any undesirable materials removed from the inner surface of the surrounding wall of the film deposition space and likewise, nor by any residual gases remaining in the film deposition space, which are often found in the known plasma CVD process, since the film deposition space, the active species generation space and the precursor generation space are separate.
However, there still exist the following problems necessary to be solved for the foregoing HR-CVD process that a film once deposited on a substrate will sometimes peeled off in the course of continuing the film-forming operation, this problem often occurs particularly in the case of forming a polycrystalline deposited film; a desired high deposition rate is rarely attained; it is difficult to repeatedly form a desired deposited film having satisfactory characteristics; it often fails to form a desired deposited film when the film-forming conditions are changed aiming at providing desired characteristics for the film to be obtained; and the process control in order to attain mass production of a desired deposited film with reproducibility is difficult.
Accordingly, there is a demand to eliminate the foregoing problems and to improve the aforementioned HR-CVD process so that a desired deposited film having a wealth of many practically applicable characteristics may be effectively and stably formed without occurence of the above problem of film peeling-off at a high deposition rate and such desired deposited film may be repeatedly mass-produced.